FilesExpand file tree

 master

/

observer.py

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

100 lines (74 loc) · 2.33 KB

 master

/

observer.py

Copy path

Top

File metadata and controls

• Code
• Blame

100 lines (74 loc) · 2.33 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

"""

http://code.activestate.com/recipes/131499-observer-pattern/

*TL;DR

Maintains a list of dependents and notifies them of any state changes.

*Examples in Python ecosystem:

Django Signals: https://docs.djangoproject.com/en/2.1/topics/signals/

Flask Signals: http://flask.pocoo.org/docs/1.0/signals/

"""

class Subject:

def __init__(self):

self._observers = []

def attach(self, observer):

if observer not in self._observers:

self._observers.append(observer)

def detach(self, observer):

try:

self._observers.remove(observer)

except ValueError:

pass

def notify(self, modifier=None):

for observer in self._observers:

if modifier != observer:

observer.update(self)

class Data(Subject):

def __init__(self, name=''):

Subject.__init__(self)

self.name = name

self._data = 0

@property

def data(self):

return self._data

@data.setter

def data(self, value):

self._data = value

self.notify()

class HexViewer:

def update(self, subject):

print('HexViewer: Subject {} has data 0x{:x}'.format(subject.name, subject.data))

class DecimalViewer:

def update(self, subject):

print('DecimalViewer: Subject %s has data %d' % (subject.name, subject.data))

def main():

"""

>>> data1 = Data('Data 1')

>>> data2 = Data('Data 2')

>>> view1 = DecimalViewer()

>>> view2 = HexViewer()

>>> data1.attach(view1)

>>> data1.attach(view2)

>>> data2.attach(view2)

>>> data2.attach(view1)

>>> data1.data = 10

DecimalViewer: Subject Data 1 has data 10

HexViewer: Subject Data 1 has data 0xa

>>> data2.data = 15

HexViewer: Subject Data 2 has data 0xf

DecimalViewer: Subject Data 2 has data 15

>>> data1.data = 3

DecimalViewer: Subject Data 1 has data 3

HexViewer: Subject Data 1 has data 0x3

>>> data2.data = 5

HexViewer: Subject Data 2 has data 0x5

DecimalViewer: Subject Data 2 has data 5

# Detach HexViewer from data1 and data2

>>> data1.detach(view2)

>>> data2.detach(view2)

>>> data1.data = 10

DecimalViewer: Subject Data 1 has data 10

>>> data2.data = 15

DecimalViewer: Subject Data 2 has data 15

"""

if __name__ == "__main__":

import doctest

doctest.testmod()